Clutch device for fast declutching of two elements in transmission

ABSTRACT

A clutch arrangement for rapid disengagement of two elements in a transmission system when a chosen torque is exceeded. The one element is a conical shaft-end which carries a corresponding sleeve ( 1 ). The sleeve carries externally at its ends two mutually separated ball bearings ( 5 ) and a force transmission ring ( 20 ) disposed therebetween. An annular force transmission body ( 7 ) surrounds and is carried by the ball bearings and includes a pressurisable hydraulic chamber which when pressurised through the medium of a valve on said body causes a reduction in the diameter of the inner surface of the body ( 7 ) so that said body will be brought into force transmitting engagement with the outer surface of the ring. The sleeve ( 1 ) carries a dogging element ( 14 ) which is adapted to act on an element ( 10 ) carried by the body ( 7 ) for depressurising the hydraulic chamber ( 8 ) upon relative rotation between the body ( 7 ) and the sleeve ( 1 ). The arrangement is such that the ring ( 20 ) and the body ( 7 ) will pass free from each other in the pressureless state of the hydraulic chamber ( 8 ). The ring ( 20 ) is operatively connected to the sleeve, so that relative rotation between the clutch components will take place between the ring and the body when the clutch is triggered.

[0001] The present invention relates to a clutch arrangement of the kinddefined in the preamble of claim 1 and functioning to mutually disengagetwo transmission components mutually connected via said clutcharrangement. at a pre-determined moment in time.

[0002] Clutch arrangements of this particular kind are sometimes calledsafety couplings and are well from WO 97/21044 for example. Suchclutches, or couplings. are often used in transmissions with which heavyloads are transmitted, for the purpose of protecting the equipment onthe driving and/or on the driven side of the transmission against damagethat can occur if the torque transmitted through the transmission andthe clutch exceeds a threshold value. Clutches of this particular kindshall break the load transmission with the minimum of damage to theclutch or coupling itself, so that the clutch can be replaced quicklyand easily and/or repaired.

[0003] However, the axial length of the space incorporated foraccommodating the safety coupling is sometimes restricted. This resultsin special problems that must be solved, since it may otherwise benecessary to make significant changes in other parts of the transmissionin which the clutch shall be fitted.

[0004] One example in this respect is that each carriage of existingexpress trains of a given design has an individual electrically drivenmotor at one end of the carriage. The output shaft of the motor is shortand is coupled to a first universal joint via a long rod and a seconduniversal joint connected thereto, to a distribution gear situated atthe other end of the carriage and having two output shafts which areeach connected to drive a respective wheel in a wheel pair. Thetransmission as such has long been tested and it is, of course, suitableto mount a clutch or coupling arrangement at a position in thetransmission in which the transmission is influenced to a minimum by theinclusion of the clutch arrangement and so that the clutch arrangementis positioned conveniently with respect to fitting and removing saidarrangement to and from the system. This means that in such instancesthe clutch will preferably be mounted between the output shaft of themotor and the universal joint proximal thereto. The problem that arisesin the majority of cases is that the shaft obtains a length which issmaller than its diameter.

[0005] A further problem is that the hydraulic pressure of the clutchmust be in the order of 1000 bar. The clutch typically includes aring-shaped body that has a coaxial, cylindrical hydraulic chamber, suchthat the inner wall of the body will move radially inwards when thechamber is pressurised and thus obtain a reduction in diameter,wherewith the inner wall is brought into engagement with a sleeve thathas a conical inner surface and that is driven up onto the conical endof the motor shaft.

[0006] When the hydraulic chamber is not pressurised, the body is ableto rotate relative to the sleeve on ball bearings disposed between thebody and the sleeve as there will then be a radial clearance between thebody and the sleeve. The body includes a valve via which the hydraulicchamber is pressurised. The sleeve is a dogging element which uponrelative rotation of the body with the sleeve functions to break-off ashear-pipe that communicates with the chamber, so as to depressurise thehydraulic chamber and thereby rapidly break the power transmissionbetween the body and the sleeve so as to ensure minimum damage to theclutch and to the transmission elements connected thereto.

[0007] Because of the small axial space in which the clutch arrangementis housed, the hydraulic pressure must be high, e.g. 1100 bar, in orderto achieve requisite torque transmission. Pressures of such highmagnitudes will, of course, constitute a break-down hazard. Moreover.the difficulty in providing for comfortable fitting and removal of thebody and bearings to and from the sleeve presents a problem.

[0008] The object of the present invention is therefore to provide aclutch arrangement with which high torque transmission can be achieveddespite a short axial length, and that can be readily fitted and removedto and from the sleeve, and that can also operate at relatively lowhydraulic pressures.

[0009] This object is achieved by the invention as defined in theaccompanying claim 1.

[0010] Further embodiments of the inventive clutch arrangement will beapparent from the accompanying dependent claims.

[0011] The invention resides in positioning the ball bearings beneaththe axial ends of the body, and by operatively connecting to the sleevea ring that extends up to the inner surface of the body. The ring can beconnected operatively with the sleeve, by giving the mutual co-actingsurfaces of the ring and the sleeve a relatively high coefficient offriction, for example by forming ridges or by applying a hard powder,e.g., tungsten carbide powder, on one of the surfaces, for instance onthe inner surface of the ring. The ring will then be essentially freefrom the sleeve when the hydraulic chamber is depressurised and when thesleeve is withdrawn from the end of the shaft, so that the body, theball bearings and the ring can be readily withdrawn axially from thesleeve. The sliding surfaces of the clutch arrangement, i.e. themutually facing surfaces of the body and the ring, may be damaged as aresult of frequent activation or engagement of the clutch due toexceeding a set torque, and the heavily loaded ball bearings may also bedamaged as a result of unbalanced forces. It is therefore appropriate toreplace such components so as to bring the clutch to an operable state.

[0012] The ring may be fixedly connected to the sleeve. the constructionshould then be further developed so as to enable the bearings to bedismantled by moving them towards respective axially adjacent ends ofthe body wherewith the dogging element, which is suitably locatedaxially outwards of one of the ball bearings. should be capable of beingdismantled.

[0013] Alternatively. the ring may be removably connected to the sleevevia a spline connection or some other known type of connection, so as toenable the body with the ball bearings and the ring to be readilywithdrawn axially from the sleeve when removed from the shaft, afterhaving loosened the connection.

[0014] In a further variant of the invention. the dogging element mayinclude a hub fitted to an end-part of the sleeve so as to lock onto thesleeve when said sleeve widens as it is driven onto the conical shaftend, thereby enabling the dogging element to be readily dismantled orremoved when the sleeve has been withdrawn, wherewith the ball bearingscan be readily removed axially towards respective adjacent ends of thesleeve, whereby the ring may be fixedly to the sleeve, and whereby thesleeve and the ring constitute a replacement for restoring the clutch toan operative state. ?

[0015] In preferred embodiments, the respective axial ends of thehydraulic chamber are situated approximately in a plane that is normalto the clutch axis, containing centres for the balls of respective ballbearings. In this way, the end-part of the annular body will swing outso that the outer rings of the ball bearings are also twisted when thehydraulic chamber is pressurised, whereby the ball bearings arecontrolled and swing-in between their bearing races with no clearance orplay. This avoids so-called “brinelling” otherwise caused by balls thatlie in the gap between races bouncing against each other as a result ofexternal vibrations between the bearing rings and causing microscopicdamage thereto. Because a clutch. or coupling, according to theinvention may be in use for a considerable time (several years) beforethe clutch is triggered, such vibrational damage can develop over a longperiod of time and significantly reduce the life-time of the ballbearings, so that they will not be operable during the short period oftime that the body and the sleeve rotate relative to each other when theclutch is triggered. Because of the clearance-free clamping of the ballsof the bearings, the useful life of the ball bearings is increasedwithout needing to use ring-shaped spring elements that would encroachon the axial space required for accommodating the length of the ring inthe space at disposal for the clutch arrangement.

[0016] The invention will now be described in more detail by way ofexample and with reference to the accompanying drawing.

[0017]FIG. 1 is an axial sectioned view of a mounted safety couplingaccording to the invention.

[0018]FIG. 2 is an axial sectioned view of the coupling in conjunctionwith fitting/removing the coupling.

[0019]FIG. 3 illustrates schematically the position of the coupling in atransmission in a railway carriage of an express train.

[0020] Shown in FIG. 1 is a sleeve 1 that has a conical inner surfacewhich is driven up onto a corresponding conical outer surface of a shaftend 2. The sleeve 1 is secured by an end-plate 3 which is fixed to thefree end of the shaft end 2 by means of bolts 4. The sleeve has acylindrical outer surface which carries at its ends two axially spacedball bearings 5 that rotatably carry an annular body 7 which contains acoaxial, cylindrical hydraulic chamber 8 in the proximity of its innersurface, which is cylindrical when the chamber is pressure less.Pressurised hydraulic fluid is delivered to the chamber 8 through themedium of a valve 9 on the body 7. The body 7 has a radially projectingshear pipe 10 which communicates with the chamber 8.

[0021] A so-called dogging element 14 is attached to the sleeve 1 andhas an arm 5 which is able to strike against the pipe 10 upon relativerotation between the body 7 and the sleeve 1.

[0022] A cylindrical ring 90 extends between the bearings 5 and betweenthe sleeve 1 and body 7. The friction between the ring 20 and the sleeve1 is relatively high in relation to the friction between the ring 20 andthe body 7 when said ring and body are in contact with one another. Theinner wall 17 of the body 7, said wall being defined by the chamber 8curves radially inwards when the chamber 8 is pressurised, e.g. with apressure of 1000 bars, so as to achieve frictional engagement betweenthe intermediate wall 17 and the ring 20 and also between the ring 20and the sleeve 1.

[0023] The ring 20 is dimensioned to obtain a radial clearance of about0.1-0.5 mm to the surface of the wall 17 when there is no pressure inthe chamber 8, so that the body 7 is able to rotate freely in relationto the sleeve when the arm 15 has broken-off the shear-pipe 10, therebyrelieving the hydraulic chamber of all load.

[0024] In the case of the described embodiment, the body 7 is bolted toa jointing flange on a transmission shaft (not shown) that lies incoaxial alignment with the shaft end 2.

[0025] The friction coefficients of the inner surface and the outersurface of the ring 20 in relation to the adjacent surfaces willpreferably have the relationship

μ>(dy/di)²×μ_(y)

[0026] where dy/di are the outer diameter and inner diameter of the ringrespectively.

[0027] This enables the clutch or coupling, to be readily fitted andremoved/dismantled, by simply drawing the body from the sleeve and theball bearings, subsequent to having removed the sleeve and the elementscarried thereby from the shaft end. Moreover, the ball bearings and thering can he readily withdrawn from the sleeve in one axial direction,whereby the dogging element may thus be permanently connected to one endof the sleeve 1. Alternatively the dogging element may be removablyconnected to the sleeve. wherewith the ring may be connected to thesleeve, either formed integrally therewith or by means of a spline jointor like means.

[0028] By arranging the slip surface at a radius corresponding to theouter diameter of the ball bearings instead of at a surfacecorresponding to the inner diameter of said ball bearings, it ispossible to work with a much lower hydraulic pressure in the chamber(900 bar instead of 1100 bar in one practical application). Thisprovides a higher degree of safety and/or enables the transmission of ahigher torque.

[0029] In the FIG. 1 illustration, the dogging element has a hub whichis firmly clamped on a cylindrical surface at one end of the sleeve.This fixation of the hub is abolished when load on the sleeve is removedfor withdrawal from the shaft end so as to enable the dogging element tobe readily removed, wherewith the adjacent bearing can also be removedaxially from the sleeve even though the ring is connected to the hub.

[0030]FIG. 2 shows schematically that a hydraulic chamber cover isscrewed firmly to one end of the shaft end and that the sleeve 1 carriesa cylinder which co-acts with said cover. Located between the cover andthe cylinder wall is a ring-shaped chamber which communicates with aconnection nipple to which pressurised hydraulic fluid can be deliveredfor axial displacement of the cylinder ring relative to the cover,whereby the sleeve 1 can be driven up onto the shaft end, as shown inthe figure. Hydraulic pressure can be applied to an adjacent ringchamber via another connecting channel, for withdrawing the sleeve 1from the shaft end. FIG. 2 also shows that a nipple is fitted via thecover and the shaft end and connects with a supply channel that opensout into a peripheral groove on said shaft end. Axial displacement ofthe sleeve is facilitated by injecting oil into the ring groove and thusinto the interface between the shaft end and sleeve.

[0031]FIG. 3 is a schematic view taken from beneath a railways carriageand showing its drive transmission. wherewith an electrically drivenmotor (3600 rpm) at one end of the carriage has a short output shaftwhich is connected to a first universal joint which, in turn. isconnected to a second universal joint by means of a long, longitudinallyextending rod. The second universal joint is connected to a distributiongear located at the other end of the carriage and having output shaftsconnected to the driven wheel pair.

[0032] A clutch or coupling according to the invention can be mounted atthe output shaft of the electric motor, providing that the axial lengthof the clutch is at most about 100 mm. One embodiment of the invention.which can be used with the application shown in FIG. 3, has a weight of26 kg and provides torque transmission in the range of 10-20 kNm with anadjustment accuracy of +15/−10% and with a maximum hydraulic pressure of1000 bar.

1. A clutch arrangement for rapid disengagement of two elements in atransmission system when a chosen torque is exceeded wherein one elementis a conical shaft end that carries a corresponding sleeve (1) which inturn, carries externally at its axial ends two mutually spaced ballbearings (5) and a force transmission ring (20) disposed therebetween,wherein an annular force transmission body (7) surrounds and is carriedby said ball bearings and includes a pressurisable hydraulic chamberwhich when pressurised through the medium of a valve on said body causesthe diameter of the inner surface of the body (7) to decrease so as toattain force transmitting engagement with the outer surface of the ring.and wherein the sleeve (1) carries a dogging element (14) which isadapted to act on an element (10) carried by the body (7) for relievingthe hydraulic chamber (8) of pressure upon relative rotation between thebody (7) and the sleeve (1), characterised in that the ring (20) and thebody (7) are adapted to pass free from each other when the hydraulicchamber (8) is depressurised; and in that the ring (20) is connectedoperatively with the sleeve so that relative rotation between the clutchcomponents will take place between the ring and the body when the clutchis triggered.
 2. A clutch arrangement according to claim 1,characterised in that the ring (20) is permanently connected to thesleeve (1); and in that the dogging element (14) is releasably connectedto the sleeve.
 3. A clutch arrangement according to claim 1,characterised in that the ring (20) is releasably connected to thesleeve (1).
 4. A clutch arrangement according to claim 3, characterisedin that the ring (20) is releasably connected to the sleeve (1) througha medium of a friction joint that is established when pressurising thehydraulic chamber, and in that the friction coefficient (μ₁) withrespect to the engagement between the ring (20) and the sleeve isrelated to the friction coefficient (μ_(y)) with respect to theengagement between the ring (20) and the body (7) according to therelationship μ₁ A (dy/di)²×μ_(y), where dy is the outer diameter of thering (20) and di is the inner diameter of said ring (20).
 5. A clutcharrangement according to any one of claims 1-4, characterised in thatthe axial ends of the hydraulic chamber are situated in the region of aplane normal to the axis of the clutch arrangement, including centresfor the balls of ball bearings, whereby the wall of the hydraulicchamber (8) proximal to the ring (20) twists the outer ball bearingrings into play-less contact with the bearing balls in the pressurisedstate of the hydraulic chamber.